For repairing walls of a concrete building, for instance, loosened from or lifted off the underlying concrete body due to cracks developed therein, there has been proposed in Japanese Utility Model Application No. 27713/85 a grease gun type chemical liquid injector adapted for automatically delivering a chemical liquid through utilization of the thrust by a spring. The conventional injector has a structure in which a chemical liquid of relatively high viscosity, contained directly in the injector casing or body, is discharged by a spring-loaded piston slidably received therein. Wit this structure, however, since the piston must be removed from the injector casing along with its cap, for loading the injector with the liquid, air is naturally entrapped in the casing between the liquid and the piston head when the piston has been re-inserted into he injector body. Consequently, as the chemical liquid is forced into, for instance, a crack in a wall by the piston, the air in the casing inevitably finds its way into the liquid being delivered, and it remains in the crack in the form of bubbles, offering a serious hindrance to the crack-mending work.
Furthermore, in the case of repairing a wall lifted off the underlying concrete body by injecting the chemical liquid into the gap therebetween, air remaining in the gap is gradually driven into its innermost part and is not purged out therefrom. This leads to a substantial reduction of the injection rate, making the repair work difficult.
It is therefore an object of the present invention to provide a chemical liquid injector which is automatically purged of air entrapped between the chemical liquid and the piston head by the insertion of the piston into the injector body, permitting efficient injection of the chemical liquid.